The present invention relates to the use of propanone 1,3-disulfonic acid, also more commonly known as acetone disulfonic acid, as an esterification catalyst.
The reaction of an organic acid with an alcohol to produce the corresponding acid ester is generally well known. These esterification reactions are typically carried out in the presence of an acid catalyst. E. G. Zey in the chapter entitled "Esterification" in the Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed., Volume 9, pp. 291-310, John Wiley & Sons, New York, 1978 discloses that the most common catalysts are strong mineral acids, but other agents, such as tin salts, organo-titanates, silica gel and cation-exchange resins, are often employed. Sulfuric acid and hydrochloric acid are the classical esterification catalysts for laboratory preparations. However, alkyl chlorides may form or dehydration, isomerization, or polymerization side reactions may result when these acids are used. Sulfonic acids, such as benzenesulfonic acid, p-toluenesulfonic acid, or methanesulfonic acid, are often used in plant operations because they are less corrosive. Phosphoric acid has also been used, but it leads to rather slow reactions.
U.S. Pat. No. 3,071,604 issued Jan. 1, 1963 to A. G. Mohan et al. discloses the esterification of saturated and unsaturated fatty acids with monohydric and polyhydric alcohols. The acid catalysts which are disclosed as being effective in the esterification reactions include alkyl, aryl, or alkylaryl sulfonic acids, which include methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and dodecylbenzenesulfonic acid. Inorganic acids, such as sulfuric acid, phosphoric acid and sulfonic acid-type ion-exchange resins are also disclosed as catalysts.
Although there are several known acids which function as esterification catalysts, there is a continuing need, especially on a commerical scale, for a catalyst with a more rapid rate of ester product formation.